I wish I had photos to illustrate this post, but I don’t, it’s just something that’s been on my mind.
I’m not sure I’d ever laid eyes on a dark-phase Red-tailed Hawk before I moved to Eastern Oregon. Now I see them all the time. (At first, I’m embarrassed to admit, I think I mistook a few of them for Golden Eagles. Western raptors are still a new thing for me.) Click here for a photo of a typical Red-tailed Hawk, and here for a photo of the dark variety. Same species, two very different-looking birds.
A number of other Buteo raptors also have dark and light morphs – Swainson’s Hawks, Rough-legged Hawks, and Ferruginous Hawks are all found here and all include both dark and light birds. This variation is genetic (think of hair color in humans), and while dark birds are generally less common that light birds in every species, this varies by geography – you’re more likely to see a dark Red-tailed or Ferruginous Hawk out west, more likely to see a dark Rough-legged Hawk back east. What I want to know is, why? Is natural selection at work here, and if so, how are different color morphs adaptive for different regions?